There are many prior dispensing apparatus for blending two or more fluids during the dispensing of a fluid product. For example, Krone, et al U.S. Pat. No. 3,847,302 teaches the activation of one or more valves via energization of associated solenoids for dispensing a desired blend or grade of gasoline. Krone does not appear to teach closed loop control of the, flow rates of the products making up the ultimate blended product, but utilizes pre-set valve openings.
Buchanan U.S. Pat. No. 3,895,738 discloses a blending system for blending two products together in order to obtain a desired product for dispensing. Buchanan individually sets the rates of flow of each one of the two products for accomplishing the required blending. No feedback or closed loop operation is evident in Buchanan.
Kierbow, et al U.S. Pat. No. 4,265,266 teaches the use of proportional control valves in a blending system, and uses closed loop control via a microprocesser for controlling the rate of flow of one of the two products being blending. The valves control hydraulic motors, which in turn control pumps for pumping the fluid.
Crain, et al U.S. Pat. No. 4,538,222 teaches a system for producing a fracturing fluid consisting of water and number of different additives, wherein a microprocessor is programmed to respond to the total flow of water and each additive, and to preselected concentration values for each additive for controlling the speed of pumps associated with each additive to maintain a desired concentration of each additive in the mixture. Cox, et al U.S. Pat. No. 4,433,701 teaches a polymer mixing system including closed loop control. Cox uses a micro-processor 8 to control a gear pump 10 as a function of the error between a "processed input" and a "set point input".
Vetter, et al U.S. Pat. No. 4,440,314 teaches the control of the "dosing of at least one fluid component of a mixture of fluids. Vetter uses closed loop control in order to maintain mixing accuracy. The flow rates of two components that are to be mixed are compared for controlling the flow rate of one of these components in order to maintain a desired mixture".
Koni, et al U.S. Pat. No. 4,345,612 teaches closed loop control for mixing two gases together in a desired ratio. The flow rates of each one of the gases are measured using a pair of flow rate sensors, respectively, in combination with a microprocessor controller for controlling the valves associated with each one of the gases.
Shannon U.S. Pat. No. 4,252,253 discloses a microprocessed drink dispenser system. Although a microprocessor is used in order to control this dispenser system, no use is made of closed loop control in order to enhance the accuracy of the drink mixtures.
Goodwin U.S. Pat. No. 4,083,473 discloses a system for blending that provides either a low octane fuel, a high octane fuel, or an intermediate octane fuel that is a blend of the latter two. The system includes flow meters for providing signals indicative of the rate of flow of the low octane and high octane fuels, respectively. A control unit is responsive to the signals for adjusting a blend control valve in closed loop fashion to provide a desired blend of the low and high octane fuels.
Lombard U.S. Pat. No. 4,043,300 discloses an apparatus and circuitry for comparing the flow rates of two fluids, such as air and fuel being delivered to an engine, for controlling a valve setting the flow rate of one of the fluids, in order to maintain a desired ratio of mixing of the fluids.
Gulbrandsen U.S. Pat. No. 3,717,283 discloses a gasoline blending apparatus including electrical circuitry and electromagnetic valving means for delivering either premium fuel, low octane fuel, or a blend of the two to a nozzle. The system disclosed does not include closed loop control, and is believed to teach the opening and closing of valves to deliver either one of the three selectable octane fuels, wherein the valves are either closed or open to a predetermined opening for the orifice of the valve.
Ernyei U.S. Pat. No. 3,410,293 discloses a "in-line blending" system including digital control means for controlling a valve 14 relative to an error signal in the flow rate of two products being blended. The flow rates of each one of the products are compared in order to derive an error signal from an idolized ratio for control of the valve 14.
Gross U.S. Pat. No. 3,229,077 teaches the use of a servo valve mechanism controlled by a digital-to-analog processor for controlling the rate of flow of one of the two products in order to obtain a desired blending. Chesuay U.S. Pat. No. 4,043,300 also shows blending control via adjusting the flow rate of one of two products.